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We must not close the subflows before all the MPTCP level data, comprising the DATA_FIN has been acked at the MPTCP level, otherwise we could be unable to retransmit as needed. __mptcp_wr_shutdown() shutdown is responsible to check for the correct status and close all subflows. Is called by the output path after spooling any data and at shutdown/close time. In a similar way, __mptcp_destroy_sock() is responsible to clean-up the MPTCP level status, and is called when the msk transition to TCP_CLOSE. The protocol level close() does not force anymore the TCP_CLOSE status, but orphan the msk socket and all the subflows. Orphaned msk sockets are forciby closed after a timeout or when all MPTCP-level data is acked. There is a caveat about keeping the orphaned subflows around: the TCP stack can asynchronusly call tcp_cleanup_ulp() on them via tcp_close(). To prevent accessing freed memory on later MPTCP level operations, the msk acquires a reference to each subflow socket and prevent subflow_ulp_release() from releasing the subflow context before __mptcp_destroy_sock(). The additional subflow references are released by __mptcp_done() and the async ULP release is detected checking ULP ops. If such field has been already cleared by the ULP release path, the dangling context is freed directly by __mptcp_done(). Co-developed-by: Davide Caratti <dcaratti@redhat.com> Signed-off-by: Davide Caratti <dcaratti@redhat.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.